CN102636198B - Induction demodulation device and method based on optical fiber ring microwave photon filter - Google Patents

Abstract

A sensing demodulation device and method based on an optical fiber ring microwave photon filter relates to an optical fiber ring microwave photon filter. The sensor demodulation device is equipped with a laser diode, an electro-optical modulator, a fiber amplifier, a frequency-sweeping radio frequency signal source, a 3-dB four-port fiber coupler, a three-port optical circulator, a chirped fiber Bragg grating, a photodetector and an electric power meter . The optical fiber ring microwave photonic filter structure is used to convert the wavelength drift of the chirped Bragg fiber grating into the intensity variation of the electrical signal by using its filtering effect on electrical signals of a certain frequency, and demodulate the wavelength information. The fiber ring microwave photonic filter adopts an incoherent filter structure, which converts the wavelength variation of the fiber grating into the power variation of the modulated electrical signal, and detects the power of the modulated electrical signal. Since the required electrical signal processing chip is relatively mature, it is therefore Greatly reduces the cost and complexity of the demodulation system.

Description

Sensing demodulation device and method based on optical fiber ring microwave photonic filter

technical field

The invention relates to a fiber ring microwave photon filter, in particular to a sensor demodulation device and method based on the fiber ring microwave photon filter.

Background technique

Fiber Bragg gratings are widely used in stress, temperature and refractive index sensing systems. In the field of fiber grating sensing, it is of great significance to develop methods and low-cost equipment for quickly demodulating the wavelength variation of fiber gratings.

Traditional fiber grating demodulation methods often use optical filter demodulation methods, such as tunable F-P filter method, unbalanced M-Z fiber interferometer method and matched grating method. These methods either have higher requirements on the performance of the optical filter, and the cost is higher; or require more optical filters, the cost is higher and the structure is complicated, and it is difficult to be practical.

Chinese patent CN201392204 discloses a fiber grating sensing demodulation device based on microwave photonic filter, including broadband light source, three-port optical circulator, sensing fiber Bragg grating, electro-optic modulator, fiber amplifier, Sagnac ring, photoelectric Detector, electric power meter, two ports of the 3-dB four-port fiber coupler are optically connected to both ends of the linearly chirped fiber grating through two sections of optical fiber, and the other two ports are used as the input port and output port of the Sagnac ring . The utility model converts the wavelength variation of the fiber grating into the power variation of the modulated electrical signal, and then performs power detection on the modulated electrical signal, greatly reducing the cost and complexity of the demodulation device.

Contents of the invention

The purpose of the present invention is to provide a low-cost sensor demodulation device and method based on fiber ring microwave photon filters to address the shortcomings of existing optical demodulation technology.

The sensing demodulation device based on the fiber ring microwave photon filter is provided with a laser diode, an electro-optic modulator, a fiber amplifier, a frequency-sweeping radio frequency signal source, a 3-dB four-port fiber coupler, a three-port optical circulator, a chirp Fiber Bragg grating, photodetector and electric power meter; the laser diode is optically connected to the input end of the electro-optic modulator, the output end of the electro-optic modulator is optically connected to the input end of the fiber amplifier, and the electric drive port of the electro-optic modulator is electrically connected to the radio frequency signal source , the output end of the optical fiber amplifier is optically connected to the input port of the optical fiber ring, the output port of the optical fiber ring is optically connected to the input end of the photodetector, and the output end of the photodetector is electrically connected to the input end of the electric power meter; the optical fiber ring includes a 3-dB four-port optical fiber Coupler, three-port optical circulator and chirped fiber Bragg grating, one output port of the 3-dB four-port fiber coupler is connected to the first port of the three-port optical circulator through the first section of optical fiber, and the three-port optical circulator The second port of the optical circulator is connected to the chirped fiber Bragg grating through the second section of fiber, the output port of the three-port optical circulator is connected to an input port of the 3-dB four-port fiber coupler, and the 3-dB four-port fiber coupler's The other two ports are respectively used as the input port and output port of the optical fiber ring.

The sensing demodulation method based on the fiber ring microwave photon filter adopts the sensing demodulation device based on the fiber ring microwave photon filter, and the method includes the following steps:

1) Turn on the laser diode, the laser diode emits a laser with a wavelength of _λ0 , which is modulated by the frequency-sweeping electrical signal f through the electro-optical modulator (EOM), and then enters the fiber amplifier for amplification;

2) The amplified light enters the fiber ring, and the fiber ring is connected by an input port and an output port of a 3-dB four-port fiber coupler to a three-port optical circulator and a chirped fiber Bragg grating whose reflection peak center wavelength is λ ₀ Composition; the chirped fiber Bragg grating is a fiber-optic device that is modulated by the refractive index written in the optical fiber by ultraviolet light, and it is a reflective device that can reflect light of a certain wavelength bandwidth. Reflection at different positions of the fiber grating; 50% of the amplified light is coupled from the input port of the 3-dB four-port fiber coupler to one output port of the 3-dB four-port fiber coupler, and enters the first fiber ring 1 section of fiber, the other 50% is directly coupled to the other output port of the 3-dB four-port fiber coupler; the light entering the fiber ring passes through the three-port optical circulator and reaches the chirped fiber Bragg grating; the light passes through the linear chirped fiber Bragg grating After reflection, it goes through the optical circulator to the second section of fiber of the fiber ring, 50% of which is coupled from another input port of the 3-dB four-port fiber coupler to another output port, and the other 50% enters the fiber ring again, so that analogy;

3) The light coupled through multiple reflections of the fiber ring exits from the output end of the fiber ring and enters the photodetector, where it is converted into an electrical signal with a success rate of P _e .

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Omega;n</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;\; L</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$

Among them, P ₀ is the output light power of the laser diode, and R is the reflectivity of the chirped fiber Bragg grating, which is a quantity related to the wavelength; the wavelength of the output light of the laser diode coincides with the reflection peak wavelength of the chirped fiber Bragg grating; n is The refractive index of the fiber, L is the length of the light passing through the fiber ring; ΔL is the reflection position of the light at the chirped fiber Bragg grating; Ω is the frequency of the electrical signal, it can be seen that when the chirped fiber Bragg grating in the fiber ring When the reflection peak wavelength changes with the change of external parameters, the light wavelength of the laser diode will also change at the reflection position of the linearly chirped fiber Bragg grating. According to the above formula, the microwave frequency detected by the photodetector The power of the electrical signal will change.

The invention adopts a fiber ring microwave photon filter structure, utilizes its filtering effect on electrical signals of a certain frequency, converts the wavelength drift of chirped Bragg fiber gratings into the intensity variation of electrical signals, and thereby demodulates the wavelength information. The fiber ring microwave photonic filter is designed with an incoherent filter structure, which is not sensitive to the interference of the external environment. At the same time, compared with the traditional demodulation scheme, the demodulation method converts the wavelength change of the fiber grating into the power of the modulated electrical signal The amount of variation is used to detect the power of the modulated electrical signal. Since the required electrical signal processing chip is more mature, the cost and complexity of the demodulation system are greatly reduced.

The invention is particularly suitable for the application field of the low-cost demodulation scheme of the chirped fiber grating. It specifically relates to a fiber ring microwave photon filter, which converts the wavelength change sensed by the chirped fiber grating into the amplitude change of the modulated microwave signal, thereby demodulating the chirped fiber grating wavelength change and the external sensing parameters A method of variation and an apparatus for implementing the method.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Detailed ways

As shown in Figure 1, the embodiment of the fiber grating sensing demodulation device based on fiber ring microwave photonic filter is provided with laser diode 1, electro-optic modulator 3, fiber amplifier 4, frequency-sweeping radio frequency signal source 2, 3-dB A four-port fiber coupler 5 , a three-port optical circulator 7 , a chirped fiber Bragg grating 8 , a photodetector 10 and an electric power meter 11 . The laser diode 1 is optically connected to the input end of the electro-optic modulator 3, the output end of the electro-optic modulator 3 is optically connected to the input end of the fiber amplifier 4, the electric drive port of the electro-optic modulator 3 is electrically connected to the frequency-sweeping radio frequency signal source 2, and the fiber amplifier 4 The output end is optically connected to the input port of the fiber optic ring, the output port of the fiber optic ring is optically connected to the input end of the photodetector 10, and the output end of the photodetector 10 is electrically connected to the input end of the electric power meter 11; the optical fiber ring includes 3-dB four ports A fiber coupler 5, a three-port optical circulator 7 and a chirped fiber Bragg grating 8, one output port of the 3-dB four-port fiber coupler 5 is connected to the first port of the three-port optical circulator 7 through the first segment of optical fiber 6 , the second port of the three-port optical circulator 7 is connected with the chirped fiber Bragg grating 8 through the second section of optical fiber 9, and the output port of the three-port optical circulator 7 is connected to an input port of the 3-dB four-port fiber coupler 5 The other two ports of the 3-dB four-port fiber coupler 5 are respectively used as the input port and the output port of the fiber ring.

The specific detection method includes the following steps:

Turn on the laser diode. The laser diode emits laser light with a wavelength of _λ0 , which is modulated by the frequency-sweeping electrical signal f through the electro-optic modulator (EOM), and then enters the fiber amplifier for amplification.

The amplified light enters the fiber optic ring. The fiber ring is formed by connecting an input port and an output port of a 3-dB four-port fiber coupler with a three-port optical circulator and a chirped fiber Bragg grating with a reflection peak center wavelength of _λ0 ; the chirped Bragg fiber The grating is a fiber-optic device with refractive index modulation written in the optical fiber by ultraviolet light. It is a reflective device that can reflect light with a certain wavelength bandwidth. Different wavelengths are reflected at different positions of the chirped fiber Bragg grating. 50% of the amplified light is coupled from the input port of the 3-dB four-port fiber coupler to an output port of the 3-dB four-port fiber coupler, and enters a section of fiber in the fiber ring, and the other 50% is directly coupled To the other output port of the 3-dB four-port fiber coupler; the light entering the fiber ring passes through the three-port optical circulator to reach the chirped fiber Bragg grating; the light is reflected by the linear chirped fiber Bragg grating and then passes through the optical circulator to the fiber Another section of fiber in the ring, 50% of which is coupled from another input port of the 3-dB four-port fiber coupler to another output port, and the other 50% enters the fiber ring again, and so on;

The light coupled through the multiple reflections of the fiber ring exits from the output end of the fiber ring and enters the photodetector, where it is transformed into an electrical signal with a success rate of P _e .

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; R</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Omega;n</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;L</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$

Among them, P ₀ is the output light power of the laser diode, and R is the reflectivity of the chirped fiber Bragg grating, which is a quantity related to the wavelength; the wavelength of the output light of the laser diode coincides with the reflection peak wavelength of the chirped fiber Bragg grating; n is The refractive index of the fiber, L is the length of light passing through the fiber ring; ΔL is the position where the light is reflected by the chirped fiber Bragg grating; Ω is the frequency of the electrical signal. It can be seen that when the reflection peak wavelength of the chirped fiber Bragg grating in the fiber ring changes with the change of the external parameters, the reflection position of the linear chirped fiber Bragg grating for the light wavelength of the laser diode will also change, According to the above formula, the power of the electric signal at the microwave frequency detected by the photodetector will change.

Claims (1)

1. based on the sensing demodulation method of the fiber ring microwave photon filter, it is characterized in that adopting the sensing demodulation device based on the fiber ring microwave photon filter, the sensing demodulation device based on the fiber ring microwave photon filter is set There are laser diodes, electro-optic modulators, fiber amplifiers, frequency-sweeping radio frequency signal sources, 3-dB four-port fiber couplers, three-port optical circulators, linear chirped fiber Bragg gratings, photodetectors and electric power meters; the laser diode It is optically connected to the input end of the electro-optical modulator, the output end of the electro-optic modulator is optically connected to the input end of the fiber amplifier, the electric drive port of the electro-optic modulator is electrically connected to the frequency-sweeping radio frequency signal source, and the output end of the fiber amplifier is optically connected to the input port of the fiber ring. The output port of the optical fiber ring is optically connected to the input end of the photodetector, and the output end of the photodetector is electrically connected to the input end of the electric power meter; the optical fiber ring includes a 3-dB four-port optical fiber coupler, a three-port optical circulator and a linear chirped Bragg One output port of the 3-dB four-port fiber coupler is connected to the first port of the three-port optical circulator through the first segment of fiber, and the second port of the three-port optical circulator is connected to the linear The chirped fiber Bragg grating is connected, the output port of the three-port optical circulator is connected to one input port of the 3-dB four-port fiber coupler, and the other two ports of the 3-dB four-port fiber coupler are respectively used as the input ports of the fiber ring and output ports; The sensing demodulation method includes the following steps: 1) Turn on the laser diode, and the laser diode emits a laser with a wavelength of _λ0 , which is modulated by the frequency-sweeping electrical signal f through the electro-optical modulator, and then enters the fiber amplifier for amplification; 2) The amplified light enters the fiber ring, which consists of an input port and an output port of a 3-dB four-port fiber coupler, a three-port optical circulator and a linearly chirped fiber Bragg grating with a reflection peak center wavelength of λ ₀ connected to form; the linear chirped fiber Bragg grating is a fiber-optic device modulated by the refractive index written in the optical fiber by ultraviolet light, and 50% of the amplified light is coupled to the input port of the 3-dB four-port fiber coupler The coupling ratio is one output port of the 3-dB four-port fiber coupler, and enters the first section of fiber in the fiber ring, and the other 50% is directly coupled to the other output port of the 3-dB four-port fiber coupler; enters the fiber ring The light passes through the three-port optical circulator and reaches the linear chirped fiber Bragg grating; the light is reflected by the linear chirped fiber Bragg grating and then passes through the optical circulator to the second section of fiber of the fiber ring, 50% of which are from the 3-dB four-port fiber Another input port of the coupler is coupled to another output port, and the other 50% enters the fiber ring again, and so on; 3) The light coupled by multiple reflections of the fiber ring exits from the output end of the fiber ring and enters the photodetector, where it is transformed into an electrical signal with a success rate of P _e . ${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; R</span>}}{{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.5</span>}\mathrm{<span\; class="notranslate">\; Re</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;\&Omega;n</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&Delta;\; L</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}$ Where P ₀ is the output light power of the laser diode, R is the reflectivity of the linear chirped fiber Bragg grating, the wavelength of the output light of the laser diode coincides with the reflection peak wavelength of the linear chirped fiber Bragg grating; n is the refractive index of the fiber, and L is The length that the light travels in the fiber ring; ΔL is the position where the light is reflected on the linearly chirped fiber Bragg grating; Ω is the frequency of the electrical signal.